The present invention relates to sensing systems for movable machines to detect when the machine has collided with an object, and particularly to such systems for motorized medical diagnostic equipment, such as X-ray machines.
In relatively large X-ray imaging systems, such as the one shown in U.S. Pat. No. 4,358,856, an X-ray source and a film holder are mounted on a movable gantry so that the components can be positioned at different angles with respect to the patient. For example, cardiac imaging often involves taking a series of X-ray images of a patient at various angles from the frontal projection through a plurality of oblique projections to a lateral projection, and through a plurality of head to foot angles in concert with the frontal and oblique projections. In order to position the gantry at each of the angles at which an exposure is to be taken, a series of motors move the gantry components with respect to the patient. The electrical drive circuitry for each motor is controlled by a set of switches operated by the X-ray technician.
Because the X-ray equipment is moving about a relatively immobile patient, a safeguard mechanism must be provided in the event of a collision between the moving equipment and the patient. In the past, sensor switches were mounted on various parts of the gantry which were likely to come into contact with the patient or the X-ray technician, during the operation of the equipment. In response to the sensor switches detecting a collision between the equipment and another object, the drive circuitry for the gantry motors was disabled until manually. A more advanced collision detection system automatically reversed the direction of the equipment when a collision was detected, until contact between the equipment and the object no longer was detected.
In power driven machines, it is important to provide a fail-safe mechanism which will sense when the machine has collided with an object or person and then stop the machine before any damage is done. Previous systems which merely sent a command to a motor control circuit when a collision was detected, did not provide such a mechanism as the collision could have been produced by a malfunction of that control circuit.